Methane conversion to methanol is currently in commercial operation worldwide and the classic standard technology practiced is via total oxidation using catalysts. These operations are very capital intensive, require huge pockets of methane gas and the methanol is produced through a syngas route. In addition to the need for huge capital and gas reserves, there is a large amount of carbon dioxide produced that contributes to a significant wastage of oxygen and methane itself.
In order to overcome the process inefficiencies, the capital intensity and the need for huge gas reserves, an alternative process, namely partial oxidation has emerged and has been documented. This partial oxidation non-catalytic route produces valuable products: alcohols (predominantly methanol and ethanol along with higher alcohols) and aldehydes (namely formaldehyde).
Separation to recover methanol, ethanol and formaldehyde is straightforward, involves a distillation process operation and can be accomplished either in batch or continuous manner. The processing steps involve fractionating methanol and the ethanol azeotrope (95% ethanol) as two distinctive fractionating cuts, leaving behind a heel of aqueous formaldehyde (formalin) at the bottom of the still. The ethanol azeotrope is further purified to ethanol using a hydrocarbon such as xylene.
Due to the proximity of boiling points of the aqueous formaldehyde solution with the ethanol azeotrope, special care must be taken to prevent formaldehyde accumulation in the distillate while maximizing ethanol recovery. By reacting formaldehyde to different chemicals, eg urea-formaldehyde, the boiling point can be modified and separation processes simplified.
Formaldehyde is a gas at standard temperature and pressure, for this reason it is typically transported as an aqueous formaldehyde solution composed of 37% formaldehyde by weight. However, although it is encountered in a liquid solution, the formaldehyde molecule is still present and is classified as carcinogenic by the Occupational Safety and Health Association. Direct integration of the synthesis of different chemicals using formaldehyde as a feedstock within the gas-to-chemicals process facilitates product handling, eliminates toxicity issues and further permits generation of higher value products.
Accordingly, there is a need for improved methods of removing aldehydes and in particular formaldehyde from the partially oxygenated hydrocarbons.